Direct radiation vacuum tube



W. W. SALISBURY DIRECT RADIATION VACUUM TUBE June 7, 1960 2 Sheets$heet1 Filed Aug. 16, 1957 w. w. SALISBURY 2,939,998 DIRECT RADIATION VACUUMTUBE 2 Sheets-Sheet 2 June 7, 1960 Filed Aug. 16, 1957 ilnited StatesPatent F DIRECT RADIATION VACUUM TUBE Winfield W. Salisbury, Palo Alto,Calif., assignor to Zenith Radio Corporation, a corporation of DeiawareFiled Aug. 16, 1957, Ser. No. 678,606

11 Claims. (Cl. 315-4) This invention relates generally to a directradiation vacuum tube apparatus and more particularly to a directradiation vacuum apparatus in which an electron stream is projected tointeract with an electromagnetic field supported by an electricalstructure to produce radiation.

In my copending application Serial No. 533,098, filed September 8, 1955,and entitled Electromagnetic Wave Generator, which issued as U.S. PatentNo. 2,866,917 on December 30, 1958, there is described a generator inwhich oscillation and radiation is produced coherently over an area ofmany square wavelengths. An electron stream is projected through andinteracts with an electromagnetic field which is supported by a periodicstructure. Energy of translation of the electron stream is transferredto the electromagnetic field and serves to increase its intensity. Thefield radiates into space.

It is an object of the present invention to provide a direct radiationvacuum tube apparatus in which the interaction region is shielded fromexternal electric fields.

This and other objects of the invention will become more apparent fromthe following description when read in conjunction with the accompanyingdrawings.

Referring to the drawings:

Figure 1 is a perspective view of a direct radiation vacuum tubeconstructed in accordance with my invention;

Figure 2 is a cross-sectional view of a direct radiation vacuum tube;

Figure 3 is a view taken along the line 33 of Figure 2;

Figure 4 is an elevationalview partly in section of another directradiation vacuum tube;

Figure 5 is a view taken along the line 5-5 of Figure 4; and

Figure 6 is an enlarged view of a portion of an electrical structurewhich may be used in a direct radiation vacuum tube.

Electrical structures which support traveling electromagnetic waveshaving a phase and group velocity of various values are well known. Forexample, a series of resonant slots or open-ended cavities coupledtogether by means of their stray fields are capable of supporting atraveling electromagnetic wave which supports a phase velocity greaterthan the velocity of light in free space.

An electromagnetic beam is regarded as a moving ionosphere. Such astream is capable of supporting magneto-hydro-dynamic or space chargewaves which have phase velocities with respect to a stationary systemwhich are greater than the velocity of light.

If an electron stream is projected through a traveling electromagneticwave, there is interaction between the wave and the electrons. If thephase velocities of the wave and the electron stream are near oneanother, the conditions are suitable for amplification of the wave byconversion of energy of translation of the electrons to electromagneticwave energy.

At various points along the wavethe electric field components of thewave will alternate in direction, tend- 2,939,998 Patented June 7, 1960ing to accelerate the electrons in the stream and a half wavelengthlater to decelerate the electrons. Electrons moving along with theaccelerated fields speed up with respect to the mean velocity of thestream, while those which are moving in fields of decelerating fieldstend to slow down. The net elfect of the interaction is to causebunching of the electrons. If theelectron stream is sup? porting a phasevelocity which is slightly greater than the phase velocity of theelectromagnetic wave, the" electron bunches in the stream willeventually move toward regions of decelerating fields. This causestheelectron stream to slow down and lose kinetic energy whichis trans;ferred to the electromagnetic wave to amplify the same. The directradiation tube is not dependent, however,,.on physical bunching ofelectrons since all parts of the radi, ating structure contributesimultaneously to aslngle radiated wave front. It is sutficient toachieve coherent radiation that widely spaced electrons have the samerelative position and approach to similar parts of the repetitivesupporting structure at the same time. This phenomenon, which may bereferred to generically as phase bunching of the electrons, isparticularly significant at extremely high frequencies, at which theelectron density per wavelength is so small as to preclude appreciablephysical bunching of electrons within anygiven wavelength. I I Theenergy of translation which is transferred to the electromagnetic waveis in effect transferred to the slots, cavities or other configurationsof the electrical structure and serves to build up the stray fieldssupported thereby. The slots, cavities, etc., of the electricalstructure then radiate into free space. The angle of the radiation issuch that the projection of the phase velocity vector on that angle isequal to the velocity of light.

The frequency or radiation depends upon the velocityof the electronstream, the configurations of the electrical structure, and the modewhich is being excited and amplified.

.The cavities or slots may degenerate into mere scratches like those ofa difiration grating. The direction of radiation is then the same asthat of the first order spectrum for the grating at the wavelengthproduced.

If stray field coupling between the various elements which form theelectrical structure is insufiicient, it may be increased by well knownmeans. For example, slots or holes may be employed to couple theresonators or cavities together. Slots or holes may also be employed tocontrol the group and phase velocity of the electromagnetic wave.

The Q of the system may be increased by providing means to intensify thestanding wave pattern at the operating frequency. This may beaccomplished by placing a partial reflector perpendicular to thedirection of radiation which sets up a standing wave pattern between therefiector and the electrical structure. 7

As described in the copending application, the radiations produced by asystem of the above character arein phase along the radiation wave frontand are, therefore, coherent radiation as contrasted to that of athermal source such as a heated black body which produces incoherentradiation. The disadvantage with incoherent radiation is that althoughit may be focused, the intensity of the image may never be greater thanthe intensity of the source. With coherent radiation, the radiation maybe concentrated into an image which is more intense than the radiatingsurface by the ratio of the area of the source to the area of the image.Theoretically, the limiting reduced size of the image is M2.Practically, the limiting size of the image is determined by thedifiraction effect of the size of the surface of origin measured inwavelengths, provided that no small aperture intervenes to intercept therays.

, predetermined values.

adjacent the structure to interact with the wave and: 'is' a'g'e appliedto dle electrical structure.

Referring now to the drawings, 1 have shown electrical structures whichare capable of supporting traveling electromagnetic waves having phaseand group velocities of An electron stream is projected collected to acollector; As a resul't'of the interaction the have isannplified. Thewave radiates coherently at an angle whichdepends "on the frequency ofoperation. .A 'pafriai reflector may be' employed to increase the Q ofthe J A lens f'sy'st'em may be employed to direct the energy to a.desired pattern. offpr'edete'rrrnned intensity. lnja'ccordance withrlrein ennon, the electrical structure is "shielde'd'frorn external electricfields and a decelerating produced between "the, Structure and thecollector thei'ebyfeiitract-energy the high velocity electron -leavingthe interaction region. 'Reirringgparticularly to Figural, a schematicperspective view-er a direct radiation vacuum tube is shown. A "suitableelectron I1 serves to project a parallel elec- Thebe'am is'accele'rated,as willbe presentl'ydescribed, and passes adjacent and parallel to thesur- T'a'c'eofthe electrical structure '13. It is then intercepted thecollector 14. A suitable gun is described in Pierce, Theory Design ofElectron. Beams (D. Van Nostrand Co Inc), pages 173-180.

The electrical structure 13 is surrounded by dielectric material 16which is transparent to the energy being The outer surfaces '17 of thedielectric material m niacs conductive to provide shielding of thestructure from electric fields. For example, the outer surface may becoated by a very thin "metallic layer such as may be produced byevaporation and which transmits a large percent-age of the radiation.The dielectric material may alo=comprisetransparent conductiveglass'orpiastic. A space 18 exists in the 'rnaterial 16 through whichthe elecbeam 12 may pass. Bringing or penetration of the electric fieldsinto the space 18 is very slight. If desired,

' grids 21 and 22 may be provided to further prevent any penetration ofelectric fields into space 18. The electrical 13 comprises a platehaving parallel slots 23 formed therein. The slots'a're spaced wherebytheir stray fields couple them together. A structure of this type supatravelling electromagnetic wave as previously which permits evacuationof the same. The tube is then and the structure supports'i'a travellingelectromagnetic wave. The stream 38 is.,projected adjacent the grooves37 and passes through the electromagnetic wave to interact therewith andamplifythe same. Surrounding the electrical structure 35 is atransparent dielectric member 41. The surface of the member 41 is coatedby a conduetive transparent material 42ypreviously described. The memberwhich surrounds the electrical structure serves merely to shield thesame from external electrical fields.

.As previously described, energy is radiated at an angle. Tofincre'a'sethe "Q oft'h'e system, a partially reflecting surface is placed in thepathof radiation and perpendicular thereto. sets up standing "waves atthe omra-ting frequency. the l'en's ,44 has a surface 46 which ispartially reflecting. A portion of the radiation is reflectedto increasemagnitude of the standing waves while the the remainder passes throughthe lens and is lenses, it is possible focused thereby. -A second iens4-7 is employed to further focus the energy to provide an image ofdesired size at a predetermined distance. It is apparent that byproperly selecting the lens system or by varying the position of .the

image. It is to be understood that although a particular lens system hasbeen described, any suitable lens system may be employed.

'The electron gun, collector, electrical structure, and

40 lens system'are-enclosed in ahevacuatedenvelopc. Such Slots orcavities have resonant. frequencies which are dependent upon theirdimensions. tron beam 12 which is projected'adjacent thestructure .13

travels through the electromagnetic Wave and interacts therewith. Energyof translation of'the electrons is transfiir r'etl to the wave, and theslots 23 radiate at an angle whichdepend's upon the velocity of theelectron stream and the size and spacing of the slots.

' Suitabl'emea'ns are provided for applying voltages to the electricalstructure and to the collector. In accord-' aneewith thc invention, ahigh positive accelerating volt- Ihe conductive The ielecan envelope isschematically s'hown at 48. The beam is maintained parallel andsubstantially ':planar by suitable electromagnetic or electrostaticfocusing. If electrostatic focusing is employed, the outer shell 48 isemployed as one of the electrodes and t'he electrical structure 35 asthe other electrode between which a suitable electric-field is applied.7 i I A high accelerating voltage is applied to the electrical structure35 and to the transparent conductive coating 50 42. Thus there isanacce'lenating field between the elec- "tron guuand surface 51 of thedielectric material which surrounds the electrical structure. Theremainderof-the conductive serves to shield the electrical structureiro'r'nstray fields. when the beam"enters -the opening 52 55 it is atits highest velocity and then travels through the i is ted to theelectrical structure and as ;a

consequence, th'e front face 26 and the grid '21 have a liigh potentialwhich serves to accelerate the electron stream. The stream then passesthrough the grid 21 into a 'region which does not have any electricfields and 's'i d'erably lower than the voltage applied to theelectrical structure. The electrons emerging irom the opening 18 throughthe grid '22 are subject to a decelerating field,

the intensity of which is dependent upon the'v oltage applied 'to thecollector. The electrons are then decelerated giving up energy to-themeans which provides the voltage. Thus it is seen that the hig'hvelocity electrons are subjected to a decelerating field which isdirectly travels :adjacent the elements 23 to the grid 22 where it 6emerges. The voltage applied to the collector 14 is-con structure andadjacent "the grooves 3'7 to. the exit 53. Someof fthe"energy oftranslation is transferred to the electromagnetic wave andiamplifiesithe same. Thus the electron s'tream..i's'slightly'decelerated fin this region.

When 'the e lectron stream emergesat 53:, it still has aIsubsta'ritialamouht tiffkine'tic energy By placing'a low voltage on arecollector-35 a decelerating field 'is'produce'd be'tween'the collector36 fandthe face 5'4 fof'the electrical structure. Tlhus the electronsTare dec'eflerated and 'give upenergy to the system supplying thefvclt'age. As a consequence, the remaining kinetic energy "is recoveredrather than being dissipated 'in the form of heat at the collector 36.The efliciency 6f he vacuum tube is substantially increasead.

It is apparent that electrical structures 'having other configurationsmay he employed. i Fo'r example, as previouslydescribedihe structure maycomprise a series of resonant cavities which are coupled "together bytheir stray fields. The coupling between: cavities ,may be increased bydorming slots between cavities or by holes to control the size andlocation of the which couple the cavities together. These slots or holesmay also be housed'to control the mode which is propagated by thestructure. The grooves may degenerate into mere scratches in whichinstance a refraction grating is formed. All such configurations of theelements of the electrical structure are understood to be included inthe scope of the invention.

In Figure 4 I have shown an electromagnetic wave generator which employsan electrical structure which is cylindrical in form. A hollow electronbeam interacts with the electromagnetic wave supported by the structure.The generator shown employs radial electric field focusing of theelectron stream.

An annular magentic structure 61 has a coil 62 wound thereon. Thestructure 61 has a magnetic field gap 63. A radial magnetic field isformed across the gap 63 through which the electrons pass. An annularelectron gun designated generally by the reference numeral 64 serves toproduce a hollow electron beam. The electron beam is then acceleratedand passes through the radial magnetic field where it acquires arotational velocity. The stream then enters into a radial electricfield.

The radial electric field arises from two sources: the charge on thecylindrical electrodes and the space charge. This field balances thecentrifugal force of the electrons to maintain the electrons in acylindrical path as they travel adjacent the electrical structure.Radial field focusing is described in detail in Fundamentals of ElectronMotion (McGraw-Hill, 1953) pages 160-163. It is of course to beunderstood that magnetic field focusing may be employed. The formationof hollow streams in this manner is well known and described in both ofthe references referred to herein.

The electrical structure 67 is provided with resonant slots 68. Theseslots may be formed annularly about the structure. For ease ofmanufacture, these slots may be formed helically as a thread. Theelectrical structure 67 has an enlarged portion 69 which forms acontinuation of the electron gun structure. The collector 71 is disposedto receive the electron stream. Cooling fins 72 are provided fordissipating the heat produced by the electrons striking the collector.

Surrounding the electrical structure there is a transparent dielectricstructure 73. The outer surface and ends of the structure are coatedwith a suitable transparent conductive coating 74 of the type previouslydescribed. The hollow electron stream travels adjacent to the electricalstructure 68 through the cylindrical opening between the structure andthe dielectric material. If desired, grids 75 and 76 may be provided atthe ends of the structure to prevent fringing or penetration of electricfields into the opening 77. The electron stream interacts with theelectromagnetic wave supported by the structure to amplify the same toproduce coherent radiation.

A lens system may be employed to focus the energy which is radiated bythe structure. The lens system may comprise any suitable number oflenses and may be adjustable to control the focal distance and size ofthe image. For example, the lens system may comprise annular lenses 81,82 and 83. The lens 81 has its surface 84 coated whereby a portion ofthe radiated energy is reflected to increase the Q of the system. Thesurface 84 is placed perpendicular to the direction of radiation. Thecomplete structure is enclosed in the metallic envelope 86. Thecylindrical electrical structure 67 and the outer envelope 86 areappropriately charged to produce the desired focusing field.

If desired, the electrical structure may be hollow as shown. The vacuumtube may then be sighted through the hollow portion. A suitable eyepiece 87 and obiectivtle1 lens system 88 may be provided to form atelescopic sig t.

Although I have described planar and cylindrical structures which serveto support electromagnetic waves, it

6 should be understood thatthe structure may take other forms. Theelectron stream is then designed to pass adjacent to as much of thesurface of the structure as possible for maximum radiation. For example,it may be desirable in certain instances to design a structure having atruncated conical shape.

Again, the accelerating voltage is applied to the electrical structure67 to accelerate the electrons which enter the cylindrical opening 77.The electrons interact with the electromagnetic wave supported by theelectrical structure and then emerge at the end 76. The interactingregion is shielded from electric fields by dielectric structure 73, theouter surface of which has a transparent conductive coating 74. Asuitable decelerating voltage is applied between the electricalstructure and the collector whereby the electrons are decelerated andenergy is recovered therefrom.

I claim:

1. A direct radiation vacuum tube comprising: an electron gun fordeveloping a stream of electrons; a collector spaced from said gun anddisposed to intercept said electron stream; an electrical structureserving to support an electromagnetic wave disposed between said gun andsaid collector, said electromagnetic wave interacting with said electronstream whereby the wave is amplified and coherently radiated directlyfrom the interacting region; a member of dielectric material transparentto said electromagnetic wave substantially surrounding said electricalstructure and closely circumscribing said electron stream throughout asubstantial portion of its path from said electron gun to saidcollector, said dielectric member being provided with a conductive outersurface transparent to said electromagnetic wave for shielding theinteracting region from electric fields; and means for focusing saidcoherently and directly radiated electromagnetic wave to a distant areaexternal to said tube.

2. A direct radiation vacuum tube as in claim 1 wherein said electricalstructure comprises a plurality of coupled resonant cavities.

3. A direct radiation vacuum tube as in claim 1 wherein said electricalstructure comprises a plurality of coupled slots. 4

4. A direct radiation vacuum tube as in claim 1 wherein said electricalstructure comprises a diffraction gratmg. 7

5. A direct radiation vacuum tube comprising an annular electron gunserving to develop a hollow cylindrical stream of electrons, a collectorspaced from said gun and disposed to intercept said stream, acylindrical electrical structure serving to support electromagneticwaves disposed between said gun and collector, said electron streamserving to interact with said electromagnetic waves to amplify the sameand produce electromagnetic energy, coherently radiated directly fromthe interacting region, a hollow cylindrical dielectric meanstransparent to said electromagnetic energy surrounding and spaced fromsaid electrical structure, a conductive surface transparent to saidelectromagnetic energy formed on said dielectric means and serving toshield the interacting region from electric fields, and means forfocusing the coherently and directly radiated electromagnetic energy toa distant area external to said tube.

6. A direct radiation vacuum tube as in claim 5 wherein said electricalstructure comprises a plurality of coupled resonant cavities.

7. A direct radiation vacuum tube as in claim 5 wherein said electricalstructure comprises a plurality of coupled slots.

8. A direct radiation vacuum tube as in claim 5 wherein said electricalstructure comprises a difiEraction grating.

9. A direct radiation vacuum tube comprising: an electron gun fordeveloping a stream of electrons; a collector spaced from said gun anddisposed to intercept said stream; an electrical structure serving tosupport an electromagnetic wave disposed between said gun and collector,said electromagnetic wave inter-acting with the electron stream wherebythe wave is amplified and coherently radiated direct y qfror-n'theinteracting region; a member of dielectricrnater-ialtransparent to saidelectromagnetic wave substantially surrounding said electrical 7structure and provided with a conductive outer surface transparent tosaid electromagnetic wave for shielding the interacting region fromelectric fields; and a partially reflecting .lens system for focusingthe coherently and directly radiated electromagnetic wave and-increasing the Q of the system.

.10, A direct radiation vacuum tube as in :claim 9 .including an inputgrid disposed between the dielectric meniber and the structure at thegun end of the structure, and an output grid disposed between thedielectric member and the structure and located, at the collector end ofthe structure, said grids serving to further shield the-interactingregion from electric fields. Q llwA direct radiation vacuum tubecomprising an annular electron :gun serving to develop a hollow[cylindrical stream of electrons, a collector spaced from said gun anddisposed to intercept said stream, a cylindrical elem trical' structureserving to support electromagnetic waves disposed between said gun andcollector, said electron stream serving to interact with saidelectromagnetic waves to amplify the same and produce electromagneticenergy, coherently radiated directly from the interacting region,

a hollow cylindrical dielectric means transparent to electromagneticenergy surrounding and spaced tram said structure, a conductive surfacetransparent to said electromagnetic energy formed on said dielectricmeans and serving to shield the interacting reg-ion from electricfields, and a partially reflecting lens :system serving to focusthecoherently and directly radiated electromagnetic energy and increase theQ of the system. 7

References Cited in the file of this patent UNITE-D STATES PATENTSFrance e. 18,1951

